In recent years, a bottlenecking of communication networks has occurred in the portion of the network known as the access network. Bandwidth on longhaul optical networks has increased sharply through new technologies such as WDM and transmission of traffic at greater bit rates. Metropolitan-area networks have also seen a dramatic increase in bandwidth. However, the access network, also known as the last mile of the communications infrastructure connecting a carrier's central office to a residential or commercial customer site, has not seen as great of an increase in affordable bandwidth. The access network thus presently acts as the bottleneck of communication networks, such as the internet.
Power-splitting passive optical networks (PSPONs) offer one solution to the bottleneck issue. PSPONs refer to typical access networks in which an optical line terminal (OLT) at the carrier's central office transmits traffic over one or two downstream wavelengths for broadcast to optical network units (ONUs). An ONU refers to a form of access node that converts optical signals transmitted via fiber to electrical signals that can be transmitted to individual subscribers and vice versa. In the upstream direction, ONUs typically time-share transmission of traffic in one wavelength.
PSPONs address the bottleneck issue by providing greater bandwidth at the access network than typical access networks. For example, networks such as digital subscriber line (DSL) networks that transmit traffic over copper telephone wires typically transmit at a rate between approximately 144 kilobits per second (KB/s) and 1.5 megabits per second (MB/s). Conversely, Broadband PONs (BPONs), which are example PSPONs, are currently being deployed to provide hundreds of megabits per second capacity shared by thirty-two users. Gigabit PONs (GPONs), another example of a PSPON, typically operate at speeds of up to 2.5 gigabits per second (GB/s) by using more powerful transmitters, providing even greater bandwidth. Other PSPONs include, for example, asynchronous transfer mode PONs (APONs) and gigabit Ethernet PONs (GEPONs).
Although PSPONs may offer much greater bandwidth than typical access networks such as DSL networks, bandwidth requirements are projected to exceed even the increased capacity offered by typical PSPONs. For example, some streaming video and online gaming applications presently require bit rates of approximately one to ten MB/s, and some IP high definition television and video-on-demand systems presently require bit rates of approximately twenty MB/s. Future demands for bandwidth are projected to be even greater. Thus, a need exists for an access network that provides even greater bandwidth.
Another solution to the present bottlenecking issue that would also satisfy demand for bandwidth for many years to come is using wavelength division multiplexing passive optical networks (WDMPONs). These networks comprise access networks in which each ONU receives and transmits traffic over a dedicated downstream and upstream wavelength, respectively. By transmitting traffic over dedicated wavelengths, WDMPONs dramatically increase network capacity over existing networks (including typical PSPONs). However, WDMPONs tend to be very expensive compared to PSPONs, the technological risks of deployment of WDMPONs are very high, and WDMPONs provide much more bandwidth than is presently demanded. Thus, a need exists for a seamless upgrade solution from PSPON that is more cost-effective than WDMPON.